How to use jhead or exiftool to add a time stamp to a jpg image

If the jpg image doesn't have exif header you need to create it first:
jhead -mkexif
Then enter the time stamp data:
jhead -ts2009:08:15-10:30:00

Apart from jhead (http://www.sentex.net/~mwandel/jhead/), there is another frequently used tool to edit exif data: exiftool (https://www.sno.phy.queensu.ca/~phil/exiftool/). When you execute exiftool to display the exif data, you get a list like this:
user@laptop:~$ exiftool IMG_001.jpg
ExifTool Version Number : 10.80
File Name : IMG_001.jpg
[...]
Date/Time Original : 2018:09:02 13:20:13
Create Date : 2018:09:02 13:20:13
[...]

However, in order to modify a value you need to address the individual tag and the tag name that the command line expects is NOT the same that is given in the list (the tag for "Create Date" is e.g. "CreateDate"):
exiftool -CreateDate='2009:11:32 09:11:24.991000' IMG_001.jpg

Exiftool is probably the most capable tool, but for the same reason, it is not the most easy to use.
IN order to remove all exif data, try:
exiftool -all=IMG_001.jpg